At maturity, Ross Seals are the smallest of the four Antarctic phocids. Based on a small sample of measured animals, Ross Seal males reach 1.68-2.09 m in length and 129-216 kg and females are slightly larger at 1.96-2.5 m in length and 159-204 kg. It is estimated that pups are about one metre and 16 kg at birth; eight suckling pups examined in November were 109-138 cm in length and 40-75 kg. Age at sexual maturity is thought to be three to four years for females and two to seven years for males (Ray 1981). Adults reach final body size at approximately nine years of age and can live to at least 20 years (Skinner and Klages 1994).

Most pups are born in November, with a peak from early to mid-November (Southwell et al. 2003). Weaning takes place at about one month of age, although little is known of the relationship between mother and pup. Nursing pups have been seen swimming between ice floes so they appear to be aquatic to some degree. Mating is thought to occur in the water, but has not been observed. Although this species has been presumed to be polygynous, genetic studies do not support this hypothesis and indicate a monogamous mating system (Curtis et al. 2011). Moulting is believed to occur in January, at which time many Ross Seals appear to fast (Skinner and Klages 1994), and moulting seals can form large aggregations on ice floes. During summer Ross Seals exhibit a diel haulout pattern with most seals hauled out on the ice at midday (Ray 1981, Bengtson and Stewart 1997, Southwell 2003). Satellite tracking suggests that Ross Seals are pelagic foragers, spending months in the open ocean foraging in association with the Antarctic Polar Front  and returning to the pack-ice to breed in October-November (Blix and Nordøy 2007).

Recent work using electronic devices to monitor at-sea behaviour of Ross Seals has revealed that the species dives continuously throughout the day (average of 108 dives per day), frequently reaching depths of 100–300 m, and displays a clear diel pattern in their diving depth. The deepest dive recorded for the species was 792 m, while the longest dives were over 30 minutes in duration (Blix and Nordøy 2007). The diet of Ross Seals is largely unknown, but the limited available data indicate that they eat mostly squid, with lesser amounts of fish and some invertebrates including krill (Ray 1981, Southwell et al. 2012). Skinner and Klages (1994) identified only Antarctic Silverfish (Pleurogramma antarcticum) in 20 animals examined; no other fish were present. Several species of squid were also recorded in this latter study, but many stomachs were empty when the animals were collected in January, suggesting that this species eats little or fasts entirely during the post-breeding moult period.

Killer Whales and Leopard Seals are presumed to be predators of the Ross Seal.

Ross Seals have a circumpolar distribution in Southern Ocean waters surrounding Antarctica. In the summer, they are usually seen in dense consolidated pack ice where they haul out to breed, moult and rest. Satellite tracking suggests that Ross Seals spend several months each year foraging in the open ocean in association with the Antarctic Polar Front (Blix and Nordøy 2007). Vagrants have been reported from many sub-Antarctic islands including the South Sandwich Islands, the South Orknies, and Falkland, Scott, Kerguelen and Heard Islands, as well as from southern Australia (Rice 1998, Thomas 2002).

Ross seals are protected by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals, and are not listed as threatened or endangered on any national Red List.